Foods are subjected to chemical and biological processes which change their composition and which may also produce substances that are harmful to health. Foods may, for example, oxidize or they may be modified by enzymes and microorganisms, e.g. mould fungi. These processes must be prevented or at least delayed within the desired shelf life so that foods can be eaten safely by the consumer and so that they can be transported, and will have the longest possible shelf life.
One possibility of doing this is to add large amounts of sugar or salt to the respective foods or to dry them so as to remove water therefrom, whereby the development of microorganisms, such as mould fungi or bacteria, will be impeded. Also an addition of alcohol or vinegar, an addition of preservatives as well as cooling slowdown the development of microorganisms and reduce the activity of enzymes. Furthermore, also a heat treatment can be carried out so as to kill microorganisms and deactivate harmful enzymes. During pasteurization the foodstuff is heated to a temperature below 100° C. for a certain period of time. The comparatively resistant bacterial spores remain, however, germinable during such treatment, and there is the risk that also important nutrients and flavours will be destroyed by the heat treatment.
Another method of increasing the shelf life of foods consists of filling the foods into a gas-tight package and evacuating the package before it is closed. If necessary, the package may also have added thereto a protective gas or protective gas mixtures, e.g. with nitrogen or CO2. Also the expulsion of air, e.g. of oxygen, has the effect that the activity of enzymes or microorganisms is slowed down.
A method which has hitherto hardly been used, at least not on an industrial scale, is the high-pressure treatment of foods. In the case of this method, a foodstuff, which has normally already been packaged, is subjected to very high pressures of typically 400 MPa to 600 MPa for a certain period of time, e.g. for a few minutes. These high pressures have the effect that harmful microorganisms in the foodstuff will be destroyed and killed, whereas comparatively small molecules, such as vitamins, which determine the flavour and the nutritional value of the foodstuff, are hardly influenced by the high-pressure treatment. As regards meat products, the shelf life may thus be increased e.g. by a factor of 6 to 10 in comparison with the non-treated product.
In comparison with heat treatment, high-pressure treatment has various advantages. For example, there is hardly any change in flavour and the vitamin content of the foodstuff is, after a high-pressure treatment, in some cases more than twice as high as after a heat treatment. In addition, some heat-sensitive products, e.g. seafood, do not allow any heat treatment at all. Pathogenic germs, such as listeria, can be killed reliably, so that food safety will be increased. High-pressure treatments can, however, also be used for purposefully influencing the internal structure of the food, so that new product possibilities, e.g. through gelatinizing of fruit preparations without heat, are obtained. Finally, the high-pressure treatment technology has already been acknowledged in many countries as (food) safe.
When packaged food is high-pressure treated, the process conditions may lead to problems with the packaging. Optically disadvantageous modifications as well as damage may occur. Problems arise especially in the case of packages containing a protective gas atmosphere, due to the highly compressible amount of gas in the package. This is also a reason for the fact that, up to now, the packages used for high-pressure treatment have predominantly been vacuum packages.
The inactivation of microorganisms as well as the structural modification of food components are described, for example, in EP 0 588 010 A1, EP 0 689 391 B1, EP 0 752 211 B1, EP 1 100 340 B1, DE 42 26 255 A1, or DE 37 34 025 C2. EP 1 112 008 B1, EP 1 201 252 B1, DE 196 49 952 A1, DE 197 38 800 A1, DE 199 39 677 A1, and DE 26 11 389 A1 describe the effects of high-pressure treatments on microbiological storage life and the safety of food. The application of high-pressure treatment especially for meat products is described in DE 198 01 031 C2, DE 196 53 677 C1, EP 0 748 592 B1, EP 0 683 986 B1, DE 101 01 958 A1, DE 10 2005 011 868 A1, or WO 2006/097248 A1.
A plant for subjecting food to a high-pressure treatment is additionally known from WO 2006/129180 A1. In this plant an autoclave is provided, which comprises a high-pressure chamber in which the food is subjected to high pressure. For building up the pressure, the autoclave must be closed. Hence, the plant cannot be operated continuously. In order to increase the throughput of the plant, it is typically operated in a batch processing mode, in which the products are introduced in the autoclave, high-pressure treated and removed from the autoclave in groups.
In order to be able to load and unload the autoclave more rapidly and to reduce thus the cycle time, the products to be treated are normally filled into a transport container. As soon as the high-pressure chamber is free, one or possibly a plurality of transport containers can be conveyed into the high-pressure chamber, e.g. by moving them by means of a slide. After the high-pressure treatment, the transport containers are removed from the autoclave, e.g. by pushing them out on the side located opposite to the inlet opening.
The transport containers, sometimes also referred to as cartridge, normally have a circular cross-section and a cylindrical shape so as to match with the normally cylindrical inner wall of the high-pressure chamber. FIG. 5 shows a cross-section of a conventional transport container 100. The transport container 100 has an outer wall 102 that imparts a circular cross-section thereto. A filling opening 103 extends over almost the entire length of the transport container 100 on the upper side thereof. Through this filling opening 103, products 104 can be filled into the transport container 100 and removed from said transport container 100.
At least when the transport container is filled by a robot, the products 104 can only be stacked vertically directly below the filling opening 103, but not in the lateral areas covered by the outer wall 102. In order to prevent the products 104 from slipping into these areas, which are covered by the upper portions of the outer wall 102, interior walls 105 can be provided, on which the products 104 abut.
The conventional transport container is disadvantageous insofar as, at least when it is filled by a robot, a substantial part of its interior volume cannot be utilized for accommodating products therein. In addition, another part of the theoretically utilizable filling volume is not filled, since the filling level must not exceed the edge of the opening 103.